Underwater Explosion Research Establishment

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View across former UNDEX site

The Underwater Explosion Research Establishment (UNDEX) was a World War II research establishment set up by the Admiralty to study the effects of underwater explosions on warships, and to determine the best way to carry out underwater attacks using explosives.

World War II

UNDEX was set up in 1943, with its headquarters based in Rosyth Naval Dockyard. Using a decommissioned vessel moored on the River Forth, researchers at the establishment carried out detailed evaluations of the effects of various underwater explosions in order to determine the structural vulnerabilities of surface ships and submarines to such attacks.

The records describe the test vessel mooring as having been between Grangemouth and Crombie Point, but this reference covers an extended area along the length of river, and may be a misinterpretation of Grangepans, which perhaps makes more sense, being located on the shore almost directly across the river from Crombie point.

Part of the establishment's facilities has been reported to have included a small explosives depot located within Tullialan Forest, Fife, sited in the area of Praybrae Wood or Pray Brae (sometimes reported as Prae Brae), with a small connecting railway mentioned. The name of the forest has since been revised to Devilla Forest on later mapping. Reference to a small railway suggests the transport of heavy items to the site, although this may only have been used during the depot's construction phase. The depot comprised a number of concrete buildings and concrete hard standings, in an area surrounded by a protective blast wall constructed from earth and wooden sleepers. Closer examination of the building remains and walls shows that these were reinforced by heavy steel plates keyed into concrete, visible in detailed photographs of the site. This additional armouring, and reports of a number of dead and damaged trees adjacent to the enclosed area are suggestive of a test site for the evaluation of explosives, rather than simple storage. A basic blast wall formed from earth over a buried munitions store would have served to deflect and disperse the effects of a single catastrophic explosion upwards, had the purpose of the site been only to store explosives. The armoured walls are also noted to be perpendicular to the ground, rather than angled, so would have done little to deflect any blast, but would instead have contained it within the enclosed space, together with any debris, and been able to do so on repeated occasions.

The possibility of carrying out evaluations of explosions tends to preclude the earlier description of this site as an explosives store, however there would still be a need to store small amounts of explosive securely, in isolation and safe from accidental detonation from any current test, and this may explain the robust building construction, and heavy metal plating (not the later NCRE blanking plates) seen in the photographs.

A munitions depot was already established at Crombie, where such material could be safely stored in bulk, and drawn down in small quantities for evaluation at the test site, or sites. An online discussion has also suggested that UNDEX might have used up outdated explosives issued from Crombie as a convenient supply, however this seems unlikely as such material would, by definition, be out of specification and therefore unreliable as a source of data for test and evaluation purposes.

Scope and content:
This series contains some papers of D E J Offord, RCNC (Royal Corps of Naval Constructors), who was the first Superintendent of the Admiralty Underwater Explosion Research Establishment (UNDEX Works) from 1943:

Administrative/biographical background:
The Naval Construction Research Establishment (NCRE) originated as the Admiralty Underwater Explosion Research Establishment (UNDEX) in 1943, becoming the NCRE in 1946. It was based in Rosyth dockyard, expanding to St Leonard's House in Dunfermline in 1949 for administrative and laboratory space. Its aims were to discover how to make warships more resistant to underwater explosions and how to make better use of underwater explosives in attack. Its work developed to include research on surface ship and submarine structures, noise reduction, and the vulnerability of ships and submarines to weapons. The establishment was controlled by the Director of Naval Construction until 1958, and then by the Director General of Ships. In 1978 it was one of the research establishments amalgamated to form the Admiralty Marine Technology Establishment (AMTE) which in turn became part of the Admiralty Research Establishment in 1984.

Site remains

All but one of the structures from the original installation at Pray Bray is reported to have been reduced to its foundations, while the remaining building is described as having had an armoured, sheet metal roof cut off using burning gear. Two metal plates, one having the letters NCRE inscribed in each corner, have been welded to the steel foundations which have been cut off at ground level. Records for the site suggest that there may be at least one underground chamber remaining within the area defined by the blast wall.